Generally, an artificial ground reef is a kind of artificial structure which may be arranged under the sea for forming habitats for various aquatic life such as fish, shellfish and seaweed, and which has been used to protect a fishing ground from drag nets or anchovy tow nets having large fishing capability and further to provide spawning ground and shelter for various fish and shellfish, fostering fish a source.
The artificial ground reef is typically classified as an immersed-arrangement type in which a structure is placed on the ocean floor surface or a float arrangement type in which the structure is moored under the sea. Meanwhile, in the prior art, various ground reefs such as waste-ship ground reef or waste-car ground reef have been used, including an assembled ground reef in which polyethylene resin or waste tire as waste material is made as a predetermined shape, however, a ground reef using such waste material has been disfavored because of ocean environmental contamination.
Here, there have been known two kinds of the immersed-arrangement ground reef among various ground reefs wherein one is a rectangular-shaped artificial ground reef, a framework of which is formed as hexahedron shape using concrete or fiber glass reinforced plastic (FRP), and the other is a hemispherical-shaped artificial ground reef in which flow passage for fish movement is formed on a hemispherical body. For arrangement of these ground reefs the rectangular-shaped and hemispherical-shaped artificial ground reefs are loaded on a barge and transported to a desired ocean region, and then these artificial ground reefs are installed to undersea using a crane tool on the barge, fostering a habitation place, spawning ground and shelter for various aquatic live such as fish, shellfish or seaweed.
However, referring to the rectangular or hemispherical-shaped artificial ground reef according to the prior art, since each ground reef is made as a simple configuration, various fish, shellfish and seaweed have difficulty in taking root and growing on a surface of the ground reef and thus even if shelter or spawning ground for fish is provided by arranging the artificial ground reef under the sea, the rooting of shellfish and seaweed which may become feed or shelter for fish is taken slowly, and further their individual numbers are very small. Accordingly, a primary object of the ground reef such as offshore farming is difficult to achieve.
Additionally, unit volume per one artificial rectangular ground reef corresponds to about 8 m3, and when about 100 units of the artificial ground reefs are arranged in a stacked manner on an undersea floor made of poor soil ground such as sandy soil, sandy and muddy soil (a soil ground mixed with sand and mud in which mud component is about 70-90% or less), or muddy soil (a soil ground having mud component of greater than 90%), the artificial ground reefs corresponding to lower 30% thereof are sunk into the sea floor to an extent of 0.3 m, 0.5 m, 1.0 m and 1.5 m or so and thus ground reef function per unit artificial ground reef on the floor is decreased to 5%, 12%, 15% and 23% in sequence. Accordingly, the artificial ground reef arranged under the sea floor made of sandy soil, sandy and muddy soil or muddy soil lacks efficiency.
Meanwhile, in the case of the hemispherical-shaped artificial ground reef, when it is arranged as one layer on a sea floor surface of a shore having a shallow water level, the hemispherical-shaped artificial ground reef sinks into the sea floor made of poor soil ground and further it may be displaced from an initial location due to high sea or tide direction. In particular, under the artificial ground reef installation business enforcement and management code, which was revised on June 2002, the artificial ground reef can be installed legally on shore waters having water level of within 10 m for business and thus a need of development for a novel artificial ground reef exists, avoiding the displacement caused from the high sea and tide direction and inducing rapid attachment thereon of various shellfish and seaweed, which primarily inhabit the sea shore, and efficiently achieving offshore farming.